Process for the manufacture of alkaline dichromates



Patented Nov. 14, 1933 rnocnss ron: THE MANUFACTURE 7 on i ALKALINE DICHROMATES 7 Jules Emile Demant, Cuise-Lamotte, France as- 'signor' to B'ozel-MaletrwSocieteindustrielle de Produits Ghimiques, Paris, France, a cor-'- pora'tion of France Q No Drawing. Application February 3, 1932, Serial No. 590,641, and 'in France March 21,,

This inventionrelates to the manufacture of alkaline. dichromates.

It .is known that hitherto the manufacture of dichromates took place in'two phases, first chrmium oxide or bodies containing chromium oxide were treated in a furnace at temperature higher than 800 C. with alka'lies with the object of the formation of mono-chromate, then the l monochromate was decomposed by means of an acid in Order to obtain the dichromate.

. Inxaccordance with the process of the present invention the dichromate is obtained in a :single phase by causing chromium oxide, its derivatives or bodies containing theysame, or metallic chromium,iits alloy or mixtures comprising chromium, to undergo an oxidizing disaggregation :by a dry method above300 Ctin the presence of bases or of mono-chromate in the quantity necessary for the reaction. The quantity of the alkali used in the process is at most 2 molecules-of NaOI-I (or a' cor-responding alkali) for' 1 molecule of Crz'O3,'no addition'of acid being'necessary. -Obviously, the reacting of one of th'e two reagents tion. In practice the temperature employed is between 300 and' 600" C. and the pressure is not higher than 20 Kg/cm As shown byth'e examples given hereinafter, good results are obtained with a temperature of 400 to 500 C. and

a pressure of approximately 5 Kg/cm 3 Two great advantages ofdthe process will be seen immediately, the obtaining of the dichromate in a single phase and'the economy of a considerable'quantity of alkaliwhich is transformed into a less valuable salt in the case of the decomposition of chromate by acid.

..It is expedient in certain cases to avoid the fusion of the product of reaction and'to this; end an excess of chromium can be used to serve as diluent, this excess being ultimately returned to the process of manufacture. It is necessary that the mixture should be very intimate. These intimate mixtures canvbe obtained by all the cus tomary-methods .and for example by a preliminary chemical reduction ofva mixture, of chromium1ox 21 Claims. (01. 22. 56)

ide or of an alloy of metallic chromium and monochromate. The alkali thus liberated is intimately distributed in the mass.

The following examples illustrate the invention the parts being by weight:--,- 1

' Example 1 .190 .parts of chromium oxide and .106 parts of sodium carbonate suitably mixed, are-treated in a furnace at 300-400 C. in the current of oxygen or air under slight pressure.

At the end of several :hours the yield of sodium dichromateexceecls 91 v The excess of chromium oxide employed is returned to the process of manufacture. 7o

A mixture composed of 100-150 parts of commercial ferrochrome containing 62.5% of chromium, and parts of caustic soda is treated for 5 hours at 400-500 C; in a current of oxygen under 5lkgs. pressure. v 1

The product obtained is treated with water; The solution contains a mixture of sodium monochromate and dichromate, the amount of .d-ichromate being from 60 to 61%.

" Example 3 v Example 4 i 160 parts of NazCrOl and 1250" parts of ferrochrome-acontaining 68.2% of chromium are heated to 400 C. in a current of hydrogen for 2 hours inorder to obtain a very intimate mixture of the reaction products.

.Then the whole is oxidized for 6 hours at 490 -C.: in a current of oxygen under 5 kgs. 'pres--.

sure and is allowed to cool in acurrent of gas under, pressure.

Theproduct obtained is lixiviated with. water. The mono-chromate used has been transformed into dichromate the amount thereof being about 97.4%. 7' g i I claim: p 1. A process for the manufacture of an; alkaline dichromate, which consists in subjecting a substance containing chromium to an oxidizing disaggregation, by the dry method, at a temperature above 300 C. and under pressure, in the presence of a compound acting as a base in the proportion at most equal to the stoechiometric quantity required to form dichromate.

2. A process for the-manufacture of an alkaline dichromate, which consists in subjecting a chromium oxide to an oxidizing disaggregation, by the dry method, at a temperature above 300 C. and under pressure, in the presence of a compound acting as a base in the proportion at most equal to the stoechiometric quantity required to form dichromate.

3. A process for the manufacture of an alkaline dichromate, which consists in subjecting metallic chromium to an oxidizing disaggregation, by the dry method, at a temperature above 300 C. and under pressure, in the presence of a compound acting as a base in the proportion at most equal to the stoechiometric quantity required to form dichromate.

4. A process for the manufacture of an alkaline dichromate, which consists in subjecting a substance containing chromium to an oxidizing disaggregation, by the dry method, at a temperature above 300 C. and under pressure in'the presence of an alkaline monochromate in the proportion at most-equal to the stoechiometric quantity required to form dichromate.

5. A process for the manufacture of an-alkaline dichromate, which consists in subjecting a chromium oxide to an oxidizing disaggregation, by the dry method, at a temperature above 300 C. and under pressure in the presence of an alkaline monochromate in the proportion at most equal to the stoechiometric quantity required to form dichromate.

6. A process for the manufacture of an alkaline dichromate, which consists in subjecting metallic chromium to an oxidizing disaggregation, by the dry method, at a temperature above 300 C. and under pressure in the presence of an alkaline monochromate in" the proportion at most equal to the stoechiometric quantityrequired to form dichromate. r

I. A process for the manufacture of an alkaline dichromate, which consists in subjecting a substance-containing chromium to the action of a gas containing oxygen, by the dry method, at a temperature above 300 C. and under pressure, in the presence of a compound acting as a base in' the proportion at most equal to the stoechiometric quantity requiredto form dichromate.

8. A process for the manufacture of an alkaline dichromate, which consists in subjecting a chromium oxide to the action of a gas containing oxygen, by the dry method, at a temperature above 300 C. and under pressure, in the presence of a compound acting as a base in the proportion at most equal to the stoechiometric quantityrequired to form dichromate.

9..A process for the manufacture of analkaline dichromate, which consists in subjecting metallic chromium to the action of a gas containing oxygen, by the dry method,.at a temperature above 300 C. and under pressure, in the presence of a compound acting as a base in the proportionat most equal to thestoechiometric quantity required to form dichromate. i I 10. A process for the manufacture of an alka line dichromate, which consists in subjecting a substance containing chromium to the action of air, by the dry method, at a temperature above 300 C. and under pressure, in the presence of a dichromate.

compound acting as a base in the proportion at most equal to the stoechiometric quantity required to. form dichromate.

11. A process for themanufacture of an alkaline dichromate, which consists in subjecting a chromium oxide to the action of air, by the dry method, at a temperature above 300 C. and under pressure, in the presence of a compound acting as a base in. the proportion at most equal to the' stoechiometric quantity required to form 12. .A process for the manufacture of an alkaline dichrornate, which consists in subjecting metallic chromium to the action of air, by the drymethod, at a temperature above 300 C. and under pressure, in the presenceof a compound acting as a base in'the proportion at most equal to the stoechiometric quantity required to form dichromate.

13. A process for the manufacture of an alkaline dichromate, which consists' in subjecting a substance containing chromium "to the-action ofa gas containing'oxygen, by the dry method,: at a temperatureabove300 C. in the presence era compound acting asabase in the proportion at most equal to the stoechiometric quantity required to form dichromate and under pressure regulated to the temperature and sufficient to prevent decomposition of the dichromate formed.

14. A process forthe manufacture of an alkaline dichromate, which consistsin subjecting a chromium oxide toithe actionof a gas contain ing oxygen, by the dry method, at a temperature 'above 300C. in thepresence of azcompound acting as a-base in the proportionat most equal to the stoechiometric quantity. required to form dichromateand under pressure regulated: to the temperature and sufficient to pr'event deoomposie tion of the dichromate formed;

15. A process for the manufacture of analkaline dichromate, whichconsistsin subjecting metallic chromiumrto the actionof a gas containing oxygen, by, the dry method,- at a..temperature above 300 C. in the presence of a com pound actingas a base in the proportionat most equal to the stoechiometric quantity requiredto form dichromate and under; pressure regulated to the temperature and sufficient to prevent-decomposition of the dichromate formed. v .16. A process for the manufacture ofuan-alkaline dichro-mate, which consists in subjecting a quantity of a substance containingchromium exceeding that theoretically requiredto an oxidizing-disaggregation, by the dry method, at a temperature above 300 C. and under pressure, in the presence of .a compoundacting'as a base in the proportion at most equal to the stoechiometric quantity required to form dichromate and ultimately returning said excess'to' the process.

1'7. A process for the manufacture of .analkaline dichromate, which consists in: subjecting a. quantity of. chromium oxide exceeding, that theoretically required to an oxidizing disaggree gation, by the dry method, at a temperature above 300C. and under pressure, in the presence of a compound acting as a base in the propor-a tion at most equal to the stoechiometric quantity required to form dichrom'ate and ultimately-re turning said excess to the-process; 18. A process for the manufacture of analkaline dichromatawhich consists in subjecting a quantity of-metallic chromium-exceeding that theoretically required to an oxidizing disaggre gatio-n, by the dry method, ata temperature above 300-Cl and under pressure, in'the presence of a; compound acting as a base in the proportion at most equal to the stoechiometric quantity required to form dichromate and ultimately returning said excess to the process.

19. A process for the manufacture of an al-v kaline dichromate, which consists in mixing an alkaline monochromate together with a substance containing chromium the amount of monochromate being in proportion at most equal to the stoechiometric quantity required to form dichromate, then reducing said mixture by chemical means to produce an intimate contact of the components thereof and subjecting the product obtained to an oxidizing disaggregation, by the dry method, at a temperature above 300 C. and under pressure.

20. A process for the manufacture of an alkaline dichromate, which consists in mixing an alkaline monochromate together with a chromium oxide the amount of monochromate being in proportion at most equal to the stoechiometric quantity required to form dichromate, then reducing said mixture by chemical means to produce an intimate contact of the components thereof and subjecting the product obtained to an oxidizing disaggregation, by the dry method, at a temperature above 300 C. and under pressure.

21. A process for the manufacture of an alkaline dichromate, which consists in mixing an alkaline monochromate together with metallic chromium the amount of monochromate being in proportion at most equal to the stoechiometric quantity required to formdichromate, then reducing said mixture by chemical means to produce an intimate contact of the components thereof and subjecting the product obtained to an oxidizing disaggregation, by the dry method, at a temperature above 300 C. and under pressure.

JULES EMILE DEMANT. 

